The invention concerns a locking-stressing-mechanism for a spring-actuated output drive device and is particularly, though not exclusively, concerned with such a device by which a high pressure produced in a fluid for example by means of a piston in a cylinder.
One aim of the invention is to adapt such a locking-stressing-mechanism to the requirements of a miniaturized high-pressure producing device.
The invention has been particularly, though not exclusively, developed for application to metered dose inhalers (MDI""s) such as are disclosed in U.S. Pat. No. 5,497,944 (derived from WO91/14468), the entire contents of both of which are incorporated herein by reference. Pressure (generally at least 50 bar) is generated in a metered amount of fluid which is discharged through a nozzle assembly having one or more very small openings e.g. in the range 25 to 500 square micrometers. Preferred nozzle assemblies are disclosed in U.S. Pat. No. 5,472,143 (and parallel WO94/07607), the entire contents of both of which are incorporated herein by reference. An energy storage means, such as a spring, is preferably manually loaded e.g. by a rotary sawtooth wedge arrangement as disclosed in U.S. Pat. No. 4,260,082 and GB Patent Application 2291135, the contents of both of which are incorporated herein by reference. A latching mechanism is generally provided to hold the spring in the loaded position and is manually releasable to pressurise the metered amount of fluid e.g. using a piston and cylinder arrangement. A reservoir and valve arrangement can be provide d for recharging the cylinder. Further details are described in PCT/EP96/04351 and parallel U.S. Pat. Ser. No. 08/726219, the entire contents of which are incorported herein by reference.
In the known locking-stressing-mechanism (W. Krause: Konstruktionselemente der Feinmechanik, Verlag Carl Hanser, Munich 1993, pages 521 to 523) previously stored energy is liberated at the required moment and converted into movement. This means for storing the mechanical energy is generally a spring which is coupled to a guided or supported component, referred to as the quick-motion portion. A locking member presents the quick-motion position from moving and liberates it in a predetermined manner.
In medical aerosol therapy, aerosols produced by atomisation or spraying of liquid medicaments are used for treating ailments of the respiratory tracts in humans or for the treatment of asthmatic conditions. For that purpose, a high pressure in respect of the fluid is required in order to produce the small droplet size necessary for the aerosol The high pressure is generally produced by a piston movable in a cylinder (DE-OS 195 36 902.5). For a miniaturised hand-operated cylindrical atomiser of that kind, it is desirable or necessary to produce a relatively high mechanical force to drive the piston within the atomiser itself.
Accordingly another aim of the invention is to develop a locking-stressing-mechanism which, even in relation to high spring forces, is simple and reliable to operate.
In accordance with one aspect of the invention, there is provided a locking-stressing-mechanism for a spring actuated output drive device, which mechanism includes a spring as a storage means for the mechanical energy which acts on an output drive member as a quick-motion portion, the movement of which is determined by the position of a locking member, a drive for stressing the spring, an upper and a lower abutment for the output drive member and a means for releasing the locking member, the device having a force step-up transmission means between the drive for stressing the spring and the spring, and an annularly arranged locking member with engaging locking surfaces.
The energy storage means is preferably a coil spring or a plate or diaphragm spring which acts as a tension spring or as a compression spring and which is preferably cylindrical.
The spring can be stressed by means of a direct drive. For that purpose the output drive flange is displaced by an axially operative external force. In the case of a high spring force, it is advantageous to provide a force step-up transmission means, for example a screw thrust transmission means, by means of which the spring is stressed by an external torque which may tie manually applied. In the case of a screw thrust transmission means, an upper housing portion and the output drive member include a single-flight or multi-flight wedge drive. Such a transmission means is arranged between the drive for stressing the spring and the spring.
The locking member can be a ring which is radially elastically deformable in itself or a rigid ring with cam projections or a rigid ring with leaf springs formed thereon or a rigid ring which can be subjected to a spring prestressing effect by one or more metal springs. The ring can be closed or open and may comprise a plurality of and preferably two parts. The locking member comprises plastics material or metal. It is arranged displaceably in a plane perpendicularly to the cylinder axis or it is deformable in said plane.
After stressing of the spring the locking surfaces of the locking member move in 0o the path of the spring or the output drive member and prevent release of the spring.
The locking member is preferably actuated by means of a release button. The button may be coupled or connected to locking member. To release the locking-stressing-mechanism a release button of this kind and therewith the locking member are generally displaced parallel to the plane of the ring, more particularly and preferably towards the cylinder axis, or the locking member is radially deformed in the plane of the ring.
The travel of the output drive member is precisely delimited by defined abutments. Preferably the drive member is a flange on a further output member.
According to another aspect of the invention, there is provided a spring-loaded drive mechanism in which an output member is mounted for linear movement against the tension of a spring between a released position and a locked position and in which there is a locking member which can be moved transversely to the direction of movement of the output member into and out of the path of an abutment means associated with the output member, wherein the locking member is substantially in the form of an open or closed ring such that the abutment means can pass through it under the action of the spring when the mechanism is released and wherein the substantially ring-like locking member may optionally be in two or more sections.
Preferably the locking member forms an optionally interrupted closed ring but it could be in the form of an open ring or yoke. It is also desirable that the locking member engages the abutment means in such a way as to minimise the risk of tilting and binding of the output member. This may for example be achieved by arranging for engagement at least at two positions which are substantially diametrically opposite each other.
Other preferred features include the following:
The spring is a helical compression spring.
The locking member snaps into alignment with the abutment means when the output member reaches the locked position.
The snap action is provided by cams associated with means for moving the output member from the released position to the locked position.
The snap action is provided by one or more springs.
The locking member is resiliently deformable so as to provide the snap action.
The locking member is arranged to be manually moved out of the path of the abutment means.
There is a force step-up transmission for moving the output means against the bias of the spring.
The transmission comprises a rotatable part with a sawtooth thrust cam.
The output member is arranged to move a piston in a cylinder to compress fluid therein.
The mechanism is part of a device for spraying fluid or, more specifically, part of a metered dose atomiser.